Pulsed doppler radar

ABSTRACT

A nanosecond pulse doppler radar adapted to hypersonic ballistic range studies is disclosed. The doppler signal is processed to give a continuous record of amplitude and phase using conventional narrow band electronics. The nanosecond pulses transmitted by the radar are obtained through TWT amplification of the amplitude modulated output of a CW X-band oscillator. The received signal is TWT amplified, range-gated with a nanosecond diode modulator and then passed through a local oscillator-mixerfilter system that selects only one PRF line for subsequent narrowband amplification and signal processing.

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d1 istates Patent 7 1 91 Mar. 19, 1974 5 1 Inventors:

Canada PULSED DOPPLER RADAR William E. Blore; Srbislav V.

A Zivimovici both of Goleta, Calitl;

:Bernard Charest, Ste-Foy, Quebec,

References Cited UNITEDiISTATES PATENTS 1 Pidhaynyuq. $511089 10/1950 Blumlein....

ThetUnited 3 States of America as 1 1 represented bytthe Secretary of the 1 1 Air Force, Washington. DC.

June 27, 1972 u. s.1c1..;... s43/s,-343/17.1 R int; C1,: G01s 9/44 Field of; Search 343/8, 1 1 7 1.1

3.009.143 11/1961 Clarke 343/8 3,028,578 4/1962 Stanton..... 3.04031 1 6/1962 Segerstrom 343/8 Primary Examiner-Maynard R. Wilbur Assistant Examiner-G. E. Montone [57] ABSTRACT A nanosecond pulse doppler radar adapted to hypersonic ballistic range studies is disclosed. The doppler signal is processed'to give a continuous record of amplitude and phase using conventional narrow band electronics. The nanosecond pulses transmitted by the radar are obtained through TWT amplification of the amplitude modulated output of a CW Xband oscilla tor. The received signal is TWT amplified, range-gated with a nanosecond diode modulator and then :passed through a local oscillator-mixer-filter system that selects only one PRF line for subsequent narrowband amplification and signal processing.

4 Claims, 1 Drawing Figure i khVQ wn QRE ATENTEHMAR 1 91914 up i 115 I ruLsEu DOPPLER R'ADARw AWCKIIGROUND or THE INVENTION lIf lVQIlllOl'l relates to pulsed doppler radar sysms, and in particular. to shortpulse radars adapted to u etectionuand measurement of radar observables of yp sonic wake phenomena.

saballisfic vehicle. reenters theearths atmosphere, r trail, is formedcaused by vehicle drag and ergyddissipation effects. The wake properties eterlmined by velocity, shape,angle of attack, and ude of the..vehiele, and are affected by dissociation nd o ization of the ablation products. Coherent radar .ehn ues permit 1 the measurement of the doppler peetra as well as. the radarcro ss section of the u herloppler power spectrum provides a measure ofrthe lrineticenergy. in thewake as a function of veloca s determined by the degree. of turbulence, and the ros s section provides a measure of the degree of min the wake. Th us radar observables are of eat pbtentialrvalue in the. study of hypersonic wake mena.

wjayw fabackgroundJCW doppler radar instruiesi in .hellistic. ranges and to study properties of as in theqlaborator where they have provided quantites ofyery useful data. Depending upon the i c {application, however, a short-pulse doppler dar may offer some significant, characteristicadvantage erela tiverlto lCW doppler .radar.-ln particular, the eteristically high range resolution and multiple iv r iange gate capabilitiesof the pulse doppler rapejrmitsimultaneousdoppler measurements (inudingiradarlicross section) on closely spaced,isolated gionsrin; the walge within the antenna beam-width, and fthus perrnit detailed correlation of. doppler radar bles from separate prescribed regions in the he e aln a; wake of a suitably large model, it is possible, for example, to simultaneously measure wake doppler centeriline and. front velocities by. appropriate placerthey radar range gates in the corresponding djalfregions. Other. advantages of a shortpulse doppler radar are: l the ability to isolate and track a cloud of scatterers feijenceyand (13;) isolation of the transmitter. signal from h doppler receiver input. Using conventionally known techniques, it is not practicable to, reduce back- ,.jshoekvrtjunnel and ballistic ranges) to the noise hie :test environment with radar, absorber material one and toprovi de adequate electrical isolationbe- M H ransmitter outputljand ireceiver input. These .oblems, characteristic of a. CW radar, can be greatly alleviated or eliminated with a pulse doppler radar.

SUMMARY OE THE INVENTION AnX-band CW klystron; phase-locked toa low frequency crystalstandard produces avCW signal at about LOdbmuIeveI. This signalris amplitudefmodulatedby diode switch .to produce one-nanosecond pulses at 15 I-I ratexlwith a 30, db on-off ratio. These pulses are mpl fiedjwto a-watt peak. pulse power level by a havebeen used for some time to measure wake in ange (2) capability tofgate out background intergroundreturn of a ground-based. wake test facility transmitter TWT and fedto. a low-sidelobe transmitting re hold are sensitive C W receiver. by the treatment calibration attenuator to a receiving TWT where it is amplified to a maximum signal level of +10 dbm, and

passed through the receiver range gate switch. The 00- currence time of the receiver gate pulse determines the position in. space of the receiver range gate.

Following this gate is a narrow-band image-rejection mixerufollowed by a narrow-band 30 MHz preamplifier and IF amplifier, driving in parallel a logarithmic amplifier and a limiter-phase detector. The outputs of two units are then displayed on conventional Oscilloscopes. The output of the 30 MHz preamplifier is a CW signal with amplitude proportional to wake Radar Cross Section and to theaverage power per line in the RF pulse The phase is proportional to model doppler velocity. The rate at which the CW signal can change to follow changes in the wake is determined by the IF amplifier bandwidth.

It is a principal object of the invention to provide a new andimproved pulsed doppler radar.

It is another object of the invention to provide an extremely short pulse doppler radar suitable for detection and measurement of radar observables in hypersonic wake phenomena.

It is another object of the invention to provide an improved pulsed doppler radar having high range resolution and multiple receiver range gate capabilities.

It is another object of the invention to provide an improved pulsed doppler radar having the ability to isolate and track a cloud of scatterers in range.

It is another object of the invention to provide an im: provedpulsed doppler radar having the :capability of gating out background interferences.

These, together with other objects, advantages and features of the invention will become more apparent from the following detailed description when taken in conjunction with the illustrative embodiment in the accompanying drawing.

DESCRIPTION OF THE DRAWINGS The sole FIGURE of the drawing is a block diagram of a nanosecond pulse radar incorporating the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the block diagram of the pulse radar as shown in FIG. 1, X-band CW klystron 1, phase-locked to a .low frequency crystal standard 33 with a commercially available phase-locking unit, pror duces a CW signal at about +10 dbm level. This signal is amplitude-modulated by diode switch 2, to produce one-nanosecond pulses at a 15 MHz rate with a 30 db on-off ratio. These pulses are amplified to a ZO-Watt peak pulse power level by transmitter TWT 3, and fed to low-sidelobe transmitting antenna 4. The reflected signal from the radar target is fed from low-sidelobe receiving antenna4 through precision calibration attenuator 34 to receiving TWT 7 where it is amplified to a maximum signal level of +10 dbm, and passed through receiver. range gate switch 8. Although separate transmitting and receiving antennas are shown a single transmit/receive antenna can of course be used. The occurrence time of the receiver gate pulse relative to the transmitted pulse is determined by phase shifter 20,

since both transmitted and receiver gate pulses were 1;

produced in pulse. generators 19, 24 that aredriven by common PRF oscillator 25 at the same 15 MHz pulse nowLLS. Pat. No. 3,764,830, filed on even da t eher ewith and herein incorporated by reference.

Following this gate is narrow-band image-rejection mixer 9 followed by narrow-band 30 MHz preamplifier l driving in parallel logarithmic amplifier l2 and limiter-phase detector 13. The output of the 30 MHz preamplifier is a CW signal with amplitude proportional to wake Radar Cross Section and to the average power per line in the RF pulse. The phase is proportional to model doppler velocity. The rate at which the CW signal can change to follow changes in the wake is determined by the preamplifier-filter bandwidth.

Waveguide isolators l7, 18, 26 and .27 have the function of inhibiting propagation of spurious signals generated in the transmitter and receiver switches.

A directional coupler l6 feeds some of the transmitted signal to image-rejection mixer 9 as local oscillator power. Another directional coupler 21 feeds some transmitted attenuator 22, phase shifter 23 and directional coupler 28, back into the front end of the receiver. This signal is used to cancel nonmoving reflections from the interior of the ballistics range which would otherwise overload the receiver. Multiplier 32 multiplies the MHZ PRF frequency to 30 MHz for use as a phase reference in the 30 MHz receiver-phasedetector.

Although the present invention has been described with reference to a specific embodiment, it is not intended that the same should be taken in a limiting sense. Accordingly it is understood that the scope of the invention in its broader aspects is to be defined by the appended claims only and no limitation is to be inferred from definite language used in describing the preferred embodiment.

We claim:

1. A pulsed doppler radar system comprising a CW electromagnetic wave source,

a frequency standard phase locked thereto,

a PRF oscillator,

a transmit/receive antenna,

amplitude modulation means connected to said PRF oscillator, the output of said CW electromagnetic wave source and to said transmit/receive antenna, said amplitude modulation means comprising a nanosecond pulse modulator and a stripline video pulse generator, said nanosecond pulse modulator being connected in series between said CW electromagnetic wave source and the transmit side of said transmit/receive antenna, and said strip-line video pulse generator being connected to actuate said nanosecond pulse modulator in response to the output of said PRF oscillator,

a receiver range gate connected to said transmit/- receive antenna,

a phase shifter connected to said PRF oscillator and to said receiver range gate,

a narrow-band image-rejection mixer connected to the output of said CW electromagnetic wave source and to the output of said receiver range gate, said receiver range gate comprising a nanosecond pulse modulator and a stripline video pulse generator, said nanosecond pulse modulator being connected in series between said image-rejection mixer and the receive side of said transmit/receive antenna, and said stripline video pulse generator being connected to actuate said nanosecond pulse modulator in response to the phase shifted output of said PRF oscillator,

a logarithmic amplifier connected to the output of said image-rejection mixer, and

a limiter-phase detector connected in parallel with said logarithmic amplifier to the output of said image-rejection mixer and to said PRF oscillator.

2. A pulsed doppler radar system as defined in claim 1 including means for displaying the output of said logarithmic amplifier and means for displaying the output of said limiter phase detector.

3. A pulsed doppler radar system as defined in claim 2 including an attenuator and a phase shifter connected in series between the receive side of said transmit/- receive antenna and said CW electromagnetic wave source.

4. A pulsed doppler radar system as defined in claim 3 including filter means connectedbetween said image rejection mixer and said logarithmic amplifier. 

1. A pulsed doppler radar system comprising a CW electromagnetic wave source, a frequency standard phase locked thereto, a PRF oscillator, a transmit/receive antenna, amplitude modulation means connected to said PRF oscillator, the output of said CW electromagnetic wave source and to said transmit/receive antenna, said amplitude modulation means comprising a nanosecond pulse modulator and a stripline video pulse generator, said nanosecond pulse modulator being connected in series between said CW electromagnetic wave source and the transmit side of said transmit/receive antenna, and said strip-line video pulse generator being connected to actuate said nanosecond pulse modulator in response to the output of said PRF oscillator, a receiver range gate connected to said transmit/receive antenna, a phase shifter connected to said PRF oscillator and to said receiver range gate, a narrow-band image-rejection mixer connected to the output of said CW electromagnetic wave source and to the output of said receiver range gate, said receiver range gate comprising a nanosecond pulse modulator and a stripline video pulse generator, said nanosecond pulse modulator being connected in series between said image-rejection mixer and the receive side of said transmit/receive antenna, and said stripline video pulse generator being connected to actuate said nanosecond pulse modulator in response to the phase shifted output of said PRF oscillator, a logarithmic amplifier connected to the output of said imagerejection mixer, and a limiter-phase detector connected in parallel with said logarithmic amplifier to the output of said image-rejection mixer aNd to said PRF oscillator.
 2. A pulsed doppler radar system as defined in claim 1 including means for displaying the output of said logarithmic amplifier and means for displaying the output of said limiter phase detector.
 3. A pulsed doppler radar system as defined in claim 2 including an attenuator and a phase shifter connected in series between the receive side of said transmit/receive antenna and said CW electromagnetic wave source.
 4. A pulsed doppler radar system as defined in claim 3 including filter means connected between said image rejection mixer and said logarithmic amplifier. 